Method of transporting saponified ethylene-vinyl ester-based copolymer pellets

ABSTRACT

There is provided a method of transporting saponified ethylene-vinyl ester-based copolymer pellets comprising maintaining an interior of a hermetic container in a state of higher pressure than ambient atmosphere during a transport of the saponified ethylene-vinyl ester-based copolymer pellets encased in the hermetic container. The method is capable of transporting dry saponified ethylene-vinyl ester-based copolymer pellets in large quantities at one time without the moisture absorption of the pellets in the course of the transport of the pellets.

The present application is a Continuation-in-Part of U.S. applicationSer. No. 14/612,705, which claims priority to U.S. ProvisionalApplication No. 62/095,238 filed Dec. 22, 2014. The disclosures of U.S.application Ser. No. 14/612,705 and U.S. Provisional Application No.62/095,238 are incorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to moisture free transport of materials,and particularly polymer materials.

2. Description of the Related Art

A saponified ethylene-vinyl ester-based copolymer (ethylene-vinylalcohol-based copolymer resin is referred to hereinafter as an “EVOHresin”) has a very strong intermolecular force because of the hydrogenbonding of hydroxyl groups present in polymer side chains. Accordingly,films made of the EVOH resin exhibit excellent gas barrier properties.For this reason, the EVOH resin and “EVOH resin pellets” obtained bypelletizing the EVOH resin is used for packaging films and packagingcontainer raw materials for water, foods, drinks and the like, and forfilms and sheets of medical product packaging materials, industrialchemical packaging materials, agricultural chemical packaging materialsand the like, or as a molding material for containers such as bottles(as disclosed in Japanese Published Patent Application No. 2011-6673,the disclosure of which is herein incorporated by reference).

In general, the EVOH resin is produced by saponifying an ethylene-vinylester-based copolymer in an alcohol solvent in the presence of acatalyst under high-temperature and high-pressure conditions, theethylene-vinyl ester-based copolymer being obtained by thecopolymerization of a fatty acid vinyl ester such as vinyl acetate andethylene. The EVOH alcohol solution under high-temperature andhigh-pressure conditions which is obtained in such a saponifying stepshall be a water/alcohol mixed solution of EVOH stable at ordinarypressure, and is extruded into a low-temperature coagulating bath havingwater as a main ingredient so as to be precipitated in the form ofstrands. The strands are cut, pelletized, and then dried, so that EVOHresin pellets are produced.

The EVOH resin and the EVOH resin pellets have hygroscopic properties.It has been known that, if the EVOH resin and the EVOH resin pelletsabsorb moisture to increase the moisture percentage (percentage ofmoisture content) thereof when in storage, the EVOH resin and the EVOHresin pellets are prone to have a poor appearance resulting from thefoaming of moisture and the like during a subsequent molding process offilms and the like. To prevent this, the aforementioned EVOH resin, ifsmall in quantity (approximately 25 kg or less), is charged and enclosedin closed transporting bags having an aluminum layer impervious tomoisture when transported in the form of pellets between plants or to acustomer or stored therein.

In the case of a large-scale step or plant in which the EVOH resinpellets are used in large quantities in a short time, on the other hand,the use of the closed transporting bags for small quantities asdescribed above for the transport and storage of the pellets results inthe decrease in transporting and operating efficiencies. When the EVOHresin pellets are required in large quantities at one time, it iscustomary to charge the aforementioned EVOH resin pellets in large-scaleclosed containers (pellet transport containers) such as large-sizedtanks, hoppers and containers, to close the containers, and to transportthe containers containing the EVOH resin pellets by using towingvehicles, trains and the like.

For actual transport, for example, storage tank parts of trucks in theform of a trailer (including a large-sized bulk loading vehicle forgranules towed by a tractor, such as a semi-trailer and a full trailer)in which a tank for powder and granular materials, a hopper and the likeare fixed (normally provided) on a bed (frame), and in the form of atank truck integrated with a tractor part, and the like are used aslarge-scale closed containers capable of loading pellets (coarsegranules) thereon, as pellet transport containers.

When a large-sized pellet transport container (a closed tank of atrailer for granules, a bulk vehicle and the like) as described above isused to transport EVOH resin pellets, the pellets which remain at a hightemperature (hot) after being subjected to hot air drying in the finalstage of the manufacturing process thereof are charged into theaforementioned closed tank and transported, with the openings of thetank sealed, for the purpose of avoiding the moisture absorption of thepellets during the transport and storage of the pellets. It has,however, been found that the method of transporting the EVOH resinpellets in the aforementioned manner might cause the aforementionedpellets to absorb moisture during the transport thereof.

As a result of the detailed observation of the state of the pellettransport container being transported, the present inventors have foundthat, as the temperature of gas within the container which has increasedby the charging of the aforementioned hot pellets decreases during thetransport of the pellets, a negative pressure resulting from heatshrinkage is developed, so that outside air enters the container. Fromthis fact, it is considered that the moisture absorbed by theaforementioned EVOH resin pellets is brought about by the outside aircontaining much moisture and coming from the outside of the pellettransport container (closed tank).

There is a danger that such moisture absorption of the EVOH resinpellets during the transport of the EVOH resin pellets causes theoccurrence of a large number of failures or poor appearances resultingfrom the foaming of moisture and the like during the molding process offilms and the like. It is therefore desirable to improve the masstransport method of the EVOH resin pellets.

SUMMARY OF THE INVENTION

In view of the foregoing, a method of transporting saponifiedethylene-vinyl ester-based copolymer pellets which is capable oftransporting dry EVOH resin pellets in large quantities at one timewithout the moisture absorption of the pellets in the course of thetransport of the pellets is provided.

In order to prevent outside air from flowing into a container during theaforementioned transport, the interior of the container is maintained ina state of higher pressure than the ambient atmosphere. Specifically, afirst aspect resides in a method of transporting saponifiedethylene-vinyl ester-based copolymer pellets comprising maintaining aninterior of a hermetic container in a state of higher pressure than theambient atmosphere during a transport of the saponified ethylene-vinylester-based copolymer pellets encased in the hermetic container.

A second aspect resides in the method of transporting the saponifiedethylene-vinyl ester-based copolymer pellets according to the firstaspect wherein a dry gas with a moisture percentage of not more than 0.8wt % is used for applying pressure to the interior of the hermeticcontainer. A third aspect resides in the method of transporting thesaponified ethylene-vinyl ester-based copolymer pellets according to thesecond aspect wherein the dry gas is nitrogen gas.

In addition, a fourth aspect resides in the method of transporting thesaponified ethylene-vinyl ester-based copolymer pellets according to thefirst aspect wherein internal pressure of the hermetic container duringthe transport is more than 1 atm and not more than 100 atm. A fifthaspect resides in the method of transporting the saponifiedethylene-vinyl ester-based copolymer pellets according to the firstaspect wherein a volume of the hermetic container is in a range of 30 to60 m³.

In addition, a sixth aspect resides in a method of transportingsaponified ethylene-vinyl ester-based copolymer pellets comprising thesteps of: encasing the saponified ethylene-vinyl ester-based copolymerpellets in a hermetic container to close the hermetic container, thehermetic container including a pressurizer for applying pressure to theinterior of the container; transporting the hermetic container to adestination; and maintaining the interior of the hermetic container in astate of higher pressure than ambient atmosphere by using thepressurizer for applying pressure to the interior of the hermeticcontainer during the transporting step.

In addition, a seventh aspect resides in the method of transporting thesaponified ethylene-vinyl ester-based copolymer pellets according to thesixth aspect wherein a dry gas with a moisture percentage of not morethan 0.8 wt. % is used for applying pressure to the interior of thehermetic container. A eighth aspect resides in the method oftransporting the saponified ethylene-vinyl ester-based copolymer pelletsaccording to the seventh aspect wherein the dry gas is nitrogen gas.

In addition, a ninth aspect resides in the method of transporting thesaponified ethylene-vinyl ester-based copolymer pellets according to thesixth aspect wherein internal pressure of the hermetic container duringthe transport is more than 1 atm and not more than 100 atm. A tenthaspect resides in the method of transporting the saponifiedethylene-vinyl ester-based copolymer pellets according to the sixthaspect wherein a volume of the hermetic container is in a range of 30 to60 m³.

To solve the aforementioned problem, it is found that the method cancompletely prevent outside air from flowing into the container duringthe aforementioned transport by maintaining the interior of the hermeticcontainer in a state of higher pressure than the ambient atmosphere.

The “dry gas with a low moisture percentage” used for the application ofpressure to the interior of the pellet transport container is selectedbased on the rate of occurrence of failures such as moisture foaming andthermal yellowing during a subsequent molding step. A gas with amoisture percentage of not more than 0.8 wt %, particularly an inert gaswith a moisture percentage adjusted to not more than 0.8 wt. %, ispreferably employed. A lower moisture percentage of the gas is morepreferably not more than 0.4 wt %, and particularly preferably closer tozero.

The method of transporting EVOH resin pellets is capable of transportingthe pellets in large quantities at one time without the moistureabsorption of the pellets even when transporting the EVOH resin pelletsby using a closed type large-sized transport container such as a trailerfor granules and a bulk loading vehicle. Thus, the pellet transportmethod improves the transport efficiency of the pellets whilemaintaining the quality of the EVOH resin pellets.

In addition, the method is characterized in comprising the steps of:encasing EVOH resin pellets in a hermetic container to close thehermetic container, the hermetic container including a pressurizer forapplying pressure to the interior of the container; transporting thehermetic container to a destination; and maintaining the interior of thehermetic container in a state of higher pressure than ambient atmosphereby using the pressurizer for applying pressure to the interior of thehermetic container during the transporting step. Thereby, the interiorof the hermetic container can be reliably maintained in a state ofhigher pressure than the ambient atmosphere by using a pressurizer, andthen, the pellets in large quantities can be transported at one timewithout the moisture absorption of the pellets in the hermetic containerwhile maintaining the quality of the EVOH resin pellets obtained in theearly stage of the encasing.

Especially, the methods are characterized in that a dry gas with amoisture percentage of not more than 0.8 wt % is used for applyingpressure to the interior of the hermetic container. Thereby, theaforementioned methods of transporting the saponified ethylene-vinylester-based copolymer pellets is capable of effectively preventingoccurrence of failures such as moisture foaming and thermal yellowingduring subsequent molding step.

Especially, the aforementioned methods is characterized in that the drygas is nitrogen gas from the viewpoint of cost and handleability.Thereby, the methods can be provided at low cost.

The aforementioned methods may be further characterized in that internalpressure of the hermetic container during the transport is more than 1atm and not more than 100 atm. Thereby, an outside air containing muchmoisture is prevented from entering the container to reliably maintainthe aforementioned EVOH resin pellets in a dry low-humidity stateobtained in the early stage of the encasing.

Especially, the method may be characterized in that a volume of thehermetic container is in a range of 30 to 60 m³. Thereby, theaforementioned methods of transporting the saponified ethylene-vinylester-based copolymer pellets are capable of transporting the pellets inlarge quantities at one time. Thus, the pellet transport methods havingthe specific volume of the hermetic container improve the transportefficiency of the pellets while maintaining the quality of the EVOHresin pellets.

The transported EVOH resin pellets do not have a poor appearance and thelike resulting from the foaming of moisture during a subsequent moldingprocess of films and the like, so that the yield of the processedproducts is improved. This improves the quality of the EVOH resin as theend product and the molded parts produced using the EVOH resin, andreduces the total costs of the molded parts produced using the EVOHresin pellets in combination with the improvement in the aforementionedpellet transport efficiency (reduction in raw material costs).

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is an external perspective view of a semi-trailer including atank for powder and granular materials.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment according to the present invention will now bedescribed in detail with reference to the drawing. It should be notedthat the present invention is not limited to the preferred embodiment.

A method of transporting EVOH resin pellets according to the embodimentis a method which is used for the transport of EVOH resin pellets inlarge quantities at one time from a manufacturing step (plant) of EVOHresin pellets to user's large-scale manufacturing step or plant in whichthe EVOH resin pellets are used in large quantities in a short time. Themethod according to the embodiment comprises maintaining the interior ofa closed type large-sized tank in a state of higher pressure than theambient atmosphere during a transport of the saponified ethylene-vinylester-based copolymer pellets encased in the closed type large-sizedtank.

The aforementioned method of transporting EVOH resin pellets will bedescribed in further detail. Examples of the closed type large-sizedtank used herein for the transport of the pellets include storage tankparts of trucks in the form of a trailer S (including a semi-trailertype towed by a tractor, a bulk loading vehicle for granules, and thelike) in which a tank T for powder and granular materials is fixed on abed (frame) as shown in the FIGURE, and in the form of a tank truckintegrated with a tractor part.

These closed type large-sized tanks T are configured to be capable ofloading (what is called, “loading in bulk”) and discharging relativelylarge granules such as pellets by air transport (pneumatictransportation). The closed type large-sized tank T used in the presentpreferred embodiment includes sealing (hermetic) means such as blockvalves mounted to a pellet insertion port and a discharge port. Ingeneral, the large-sized tank T used for the transport of pellets asdescribed above is made of stainless steel in consideration of frictionwith the pellets and the like, and a body of the tank T, except openingssuch as the aforementioned pellet insertion port, is hermeticallysealed. The volume of the aforementioned closed type large-sized tank Tgenerally used is in the range of 30 to 60 m³, and the volume of theaforementioned closed type large-sized tank T preferably used as in thisexample is on the order of 40 to 50 m³.

Examples of the pressurizing means P for maintaining an interior of thetank T in a state of higher pressure than ambient atmosphere include amechanism which includes a cylinder B or a gas generator filled with agas (dry gas) having a moisture percentage of not more than 0.8 wt % asa supply source. The pressurizing means P supplies the dry gas to thetank T at a desired flow rate by providing a pressure regulating valve(regulator) and the like between the tank T and the supply source.Thereby, the pressurizing means P can control the pressure in the Tank Teasily. Instead of that the pressurizing means P supplies the dry gas tothe tank T at the desired flow rate, the amount of gas leaked from theinterior of the tank T during the transport may be calculated, and thesame or more amount of the leaked gas may be supplied to the tank T atone time. Thereby, no pressurizing means P is required, and then, themethod can be provided at a low cost. Specific examples of the dry gassupplied to the tank T include: dry air dehumidified to a moisturepercentage of not more than 0.8 wt %; preferably inert gases such asnitrogen, argon and helium having a moisture percentage adjusted to notmore than 0.8 wt %; and particularly preferably nitrogen gas from theviewpoint of cost and handleability.

The interior of the close type large-sized tank T (the pellet transportcontainer) during the transport is maintained in a state of higherpressure than the ambient atmosphere. Specifically, it is preferablethat the internal pressure of the pellet transport container isgenerally more than 1 atm and not more than 100 atm (approximately 101.3to 10,130 kPa), preferably in the range of 1.1 to 50 atm (approximately111.4 to 5,065 kPa), more preferably in the range of 1.2 to 10 atm(approximately 121.6 to 1,013 kPa), and particularly preferably in therange of 1.3 to 3 atm (approximately 131.7 to 303.9 kPa).

Next, the EVOH resin pellets used in the aforementioned transport methodwill be described.

EVOH Resin

The EVOH resin according to the present preferred embodiment is awater-insoluble resin, and is a known resin obtained by saponifying apolymer of ethylene and a vinyl ester-based monomer. The ethylenecontent of the EVOH resin is generally 20 to 60 mol %, preferably 21 to55 mol %, particularly preferably 25 to 50 mol %, and more preferably 29to 48 mol %. When the ethylene content is too low, the resultant moldedproducts, especially stretched films, tend to degrade in gas barrierproperties and in external appearance at high humidities. On the otherhand, when the ethylene content is too high, the stretched films tend todegrade in gas barrier properties. Such an ethylene content may bemeasured, for example, pursuant to ISO 14663.

The saponification degree of a vinyl ester component in the EVOH resinis generally not less than 90 mol %, preferably, 93 to 99.99 mol %, andparticularly preferably 98 to 99.99 mol %. When the saponificationdegree is too low, the stretched films tend to degrade in gas barrierproperties and in humidity resistance and the like. The saponificationdegree of such a vinyl ester component may be measured, for example,pursuant to JIS (Japanese Industrial Standard) K6726 (in a solution suchthat the EVOH resin is uniformly dissolved in a water/methanol solvent).

The melt flow rate (MFR) of the EVOH resin (210° C., a load of 2,160 g)is generally 1 to 100 g/10 min, preferably 2 to 50 g/10 min, andparticularly preferably 3 to 30 g/10 min. When the MFR is too high, themolded products tend to degrade in mechanical strength. When the MFR istoo low, extrudability during molding tends to degrade.

The EVOH resin used in the present invention may further include astructural unit derived from comonomers to be described below. Examplesof the comonomers include: α-olefins such as propylene, isobutene,α-octene, α-dodecene and α-octadecene; hydroxy group containingα-olefins such as 3-butene-1-ol, 4-penten-1-ol and 3-butene-1,2-diol,and esterified compounds thereof; hydroxy group containing α-olefinderivatives such as acylated compounds; unsaturated carboxylic acids,and their salts, partial alkyl esters, complete alkyl esters, nitriles,amides and anhydrides; unsaturated sulfonic acids and their salts;vinylsilane compounds, vinyl chlorides; and styrenes.

Further, EVOH-based resins which are “post-modified”, e.g. urethanated,acetalized, cyanoethylated and oxyalkylenated, may be used.

Of the aforementioned modified products, an EVOH resin such that aprimary hydroxyl group is introduced into a side chain bycopolymerization is preferable because it is good in post-formability ina stretching process, vacuum forming, pressure forming and the like. Inparticular, an EVOH resin having a 1,2-diol structure in a side chain ispreferable.

The EVOH resin obtained by the aforementioned method may be used as itis. Unless the effects of the present invention are impaired, theobtained EVOH resin may contain compounding agents which are in generalcompounded into EVOH resins. Examples of the compounding agents includethermal stabilizers, antioxidants, antistatic agents, coloring agents,ultraviolet absorbers, lubricants, plasticizers, light stabilizers,surface-active agents, antimicrobial agents, drying agents,anti-blocking agents, flame retardants, cross-linkers, curing agents,foaming agents, crystal nucleating agents, anti-fogging agents,biodegradation additives, silane coupling agents, and oxygen absorbents.

Additives may be added as the aforementioned thermal stabilizers to theEVOH resin for the purpose of improving various physical properties suchas thermal stability during melt molding. Examples of the additives asthe thermal stabilizers include: organic acids such as acetic acid,propionic acid, butyric acid, lauryl acid, stearic acid, oleic acid andbehenic acid, and their salts such as alkali metal salts (sodium,potassium and the like), alkaline earth metal salts (calcium, magnesiumand the like) and zinc salts; and inorganic acids such as sulfuric acid,sulfur dioxide, carbonic acid, phosphoric acid and boric acid, and theirsalts such as alkali metal salts (sodium, potassium and the like),alkaline earth metal salts (calcium, magnesium and the like) and zincsalts. Of these, it is in particular preferable to add acetic acid,boron compounds including boric acid and its salts, acetates andphosphates.

When acetic acid is added, the amount of acetic acid is generally 0.001to 1 part by weight, preferably 0.005 to 0.2 part by weight, andparticularly preferably 0.010 to 0.1 part by weight to 100 parts byweight of the EVOH resin. When the amount of added acetic acid is toosmall, the effect of containing the acetic acid tends not to besufficiently obtained. On the other hand, when the amount of addedacetic acid is too large, it tends to be difficult to obtain uniformfilms.

When a boron compound is added, the amount of boron compound isgenerally 0.001 to 1 part by weight, preferably 0.002 to 0.2 part byweight, and particularly preferably 0.005 to 0.1 part by weight in boronequivalent (analyzed by ICP spectrometry after ashing) to 100 parts byweight of the EVOH resin. When the amount of added boron compound is toosmall, there are cases in which the effect of containing the boroncompound cannot sufficiently be obtained. On the other hand, when theamount of added boron compound is too large, it tends to be difficult toobtain uniform films.

The amount of acetate or phosphate (including hydrogen phosphate) isgenerally 0.0005 to 0.1 part by weight, preferably 0.001 to 0.05 part byweight, and particularly preferably 0.002 to 0.03 part by weight inmetal equivalent (analyzed by ICP (Inductively coupled plasma)spectrometry after ashing) to 100 parts by weight of the EVOH resin.When the amount of added acetate or phosphate is too small, there arecases in which the effect of containing the acetate or phosphate(including hydrogen phosphate) cannot sufficiently be obtained. On theother hand, when the amount of added acetate or phosphate is too large,it tends to be difficult to obtain uniform films. When two or more typesof salts are added to the EVOH resin, it is preferable that the totalamount of the two or more types of salts is within the aforementionedrange of amounts.

The method of adding acetic acid, a boron compound, acetate andphosphate to the EVOH resin is not particularly limited. Examples of themethod include: (i) bringing a porous precipitate of EVOH resin with apercentage of moisture content of 20 to 80 wt % into contact with awater solution of an additive to cause the aforementioned porous EVOHresin to contain the additive, and thereafter drying the porous EVOHresin containing the additive; (ii) causing a homogeneous solution(water/alcohol solution and the like) of EVOH resin to contain anadditive, thereafter extruding the resultant solution in the form ofstrands into a congealed liquid, cutting the obtained strands intopellets, and finally performing a drying process on the pellets; (iii)mixing the EVOH resin and an additive together, and melting and kneadingthe mixture by using an extrusion machine and the like; and (iv)neutralizing alkali (sodium hydroxide, potassium hydroxide and the like)used in the saponifying step with organic acids such as acetic acidduring the production of the EVOH resin, and adjusting the amounts ofremaining organic acids such as acetic acid and by-produced salts by awater rinse process. To conspicuously obtaining the effects of thepresent invention, the methods (i) and (ii) which are excellent indispersibility of the additive are preferable. To cause the EVOH resinto contain organic acids and their salts, the method (iv) is preferable.

Method of Producing EVOH Resin Pellets

The EVOH resin pellets according to the present invention are producedby pelletizing the EVOH resin obtained by saponifying a copolymer ofethylene and a vinyl ester-based monomer.

Typically, vinyl acetate is used as an example of the vinyl ester-basedmonomer because it is good in availability on the market and in impurityprocessing efficiency during the production thereof. Other examples ofthe vinyl ester-based monomer include: aliphatic vinyl esters such asvinyl formate, vinyl propionate, vinyl valerate, vinyl butyrate, vinylisobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinylstearate and vinyl versatate; and aromatic vinyl esters such as vinylbenzoate. Such an aliphatic vinyl ester generally has 3 to 20 carbonatoms, preferably 4 to 10 carbon atoms, and particularly preferably 4 to7 carbon atoms. These are generally used alone, but may be used incombination, as necessary.

Normal ethylene pressure polymerization may be performed as a method ofintroducing ethylene into the copolymer of ethylene and the vinylester-based monomer. The amount of ethylene to be introduced may becontrolled by the pressure of ethylene, and is generally selected fromthe range of 2.5 to 8.0 MPa although it depends on an intended ethylenecontent.

Examples of the solvent used for the copolymerization generally include:lower alcohols such as methanol, ethanol, propanol and butanol; andketones such as acetone and methyl ethyl ketone. Industrially, methanolis preferably used. The amount of usage of the solvent may be selectedas appropriate in accordance with the degree of polymerization of anintended copolymer in consideration of the chain transfer constant ofthe solvent. For example, when the solvent is methanol, S/M(solvent/monomer) is selected from the range of 0.01 to 10 (weightratio), and preferably from the range of 0.05 to 7 (weight ratio).

A polymerization catalyst is used for copolymerization. Examples of thepolymerization catalyst include: known radical polymerization catalystssuch as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide andlauryl peroxide; and low-temperature active radical polymerizationcatalysts including peroxyesters such as t-butyl peroxy neo-decanoate,t-butyl peroxy pivalate, α,α′-bis(neodecanoyl peroxy) diisopropylbenzen, cumyl peroxyneo-decanoate, 1,1,3,3,-tetramethyl butyl peroxyneodecanoate, 1-cyclohexyl-1-methylethyl peroxy neodecanoate, t-hexylperoxy neodecanoate and t-hexyl peroxypivalate, peroxydicarbonates suchas di-n-propyl peroxydicarbonate, di-iso-propyl peroxydicarbonate,di-sec-butyl peroxydicarbonate, bis(4-t-butylcyclohexyl)peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate, dimethoxybutyl peroxydicarbonate anddi(3-methyl-3-methoxybutylperoxy) dicarbonate, and diacyl peroxides suchas 3,3,5-trimethylhexanoyl peroxide, diisobutyryl peroxide and lauroylperoxide. The amount of usage of the polymerization catalyst may bearbitrarily selected in accordance with a polymerization rate althoughit depends on the type of catalyst. For example, whenazobisisobutyronitrile or acetyl peroxide is used, the amount of usageof the polymerization catalyst is preferably 0.001 to 0.2 part, andparticularly preferably 0.005 to 0.1 part per 100 parts of vinylester-based monomer.

According to the present invention, it is preferable thathydroxylactone-based compounds or hydroxycarboxylic acids coexist withthe aforementioned catalyst because they provide good color tones(closer to colorless) of the resultant resin composition. Thehydroxylactone-based compounds are not particularly limited if they arecompounds having a lactone ring and a hydroxyl group in molecules.Examples of such hydroxylactone-based compounds include L-ascorbic acid,erythorbic acid and glucono delta lactone. Preferably, L-ascorbic acidand erythorbic acid are used. Examples of the hydroxycarboxylic acidsinclude glycolic acid, lactic acid, glyceric acid, malic acid, tartaricacid, citric acid and salicylic acid. Preferably, citric acid is used.

In either batchwise or continuous scheme, the amount of usage of such ahydroxylactone-based compound or hydroxycarboxylic acid is preferably0.0001 to 0.1 part by weight, more preferably 0.0005 to 0.05 part byweight, and particularly preferably 0.001 to 0.03 part by weight per 100parts by weight of vinyl ester-based monomer. When the amount of usageis too small, there are cases in which the effect of coexistence cannotsufficiently be obtained. On the other hand, when the amount of usage istoo large, the result is the impairment of the polymerization of thevinyl ester-based monomer, which in turn is not preferable. Theintroduction of such a compound into a polymerization system is notparticularly limited. Generally, such a compound is introduced into apolymerization reaction system after being diluted with solvents such aslower aliphatic alcohols (methanol, ethanol, propanol, tert-butanol andthe like), aliphatic esters (methyl acetate, ethyl acetate and the like)including vinyl ester-based monomers, and water, or their mixedsolvents.

The reaction temperature of the copolymerization reaction is generallynot more than the boiling point of the solvent although it depends onthe solvent and pressure to be used. In general, the reactiontemperature of the copolymerization reaction is preferably 40° to 80°C., and particularly preferably 55° to 80° C. When the reactiontemperature is too low, it takes much time for polymerization. Anattempt to shorten the polymerization time necessitates a large amountof catalyst. On the other hand, when the reaction temperature is toohigh, it is difficult to control the polymerization, which in turn isnot preferable.

The polymerization time is preferably 4 to 10 hours (more preferably 6to 9 hours) in the batchwise scheme. When the polymerization time is tooshort, it is necessary to increase the polymerization temperature or toset a greater amount of catalyst. On the other hand, when thepolymerization time is too long, there arises a problem in terms ofproductivity, which in turn is not preferable. In the continuous scheme,the mean residence time in a polymerization tank is preferably 2 to 8hours (more preferably 2 to 6 hours). When the residence time is tooshort, it is necessary to increase the polymerization temperature or toset a greater amount of catalyst. On the other hand, when the residencetime is too long, there arises a problem in terms of productivity, whichin turn is not preferable.

The rate of polymerization (vinyl ester-based monomer) is set to as higha level as possible within a polymerization controllable range in termsof productivity, and is preferably 20 to 90%. When the rate ofpolymerization is too low, there arise problems in terms of productivityand in the presence of large quantities of unpolymerized vinyl acetatemonomers. On the other hand, when the rate of polymerization is toohigh, it is difficult to control the polymerization, which in turn isnot preferable.

Thus, the ethylene-vinyl ester-based copolymer is obtained by theaforementioned manufacturing method. Known methods may be employed forthe saponification of the ethylene-vinyl ester-based copolymer.

For the saponification, an alkali catalyst or an acid catalyst is used,with the aforementioned obtained copolymer dissolved in an alcohol or ahydrous alcohol. Examples of the alcohol include methanol, ethanol,propanol and tert-butanol, but methanol is most preferably used. Theconcentration of the copolymer in the alcohol is selected as appropriatein accordance with the viscosity of the system, and is generallyselected from the range of 10 to 60 wt %. Examples of the catalyst usedfor the saponification include: hydroxides of alkali metal such assodium hydroxide, potassium hydroxide, sodium methylate, sodiumethylate, potassium methylate and lithium methylate; alkali catalystssuch as alcoholate; and acid catalysts such as sulfuric acid,hydrochloric acid, nitric acid, meta-sulfonic acid, zeolite and cationexchange resin.

The amount of usage of such a saponification catalyst is selected asappropriate in accordance with a saponification method, an intendedsaponification degree and the like. When such an alkali catalyst isused, it is appropriate that the amount of usage is generally 0.001 to0.1 equivalent, and preferably 0.005 to 0.05 equivalent, based on thetotal quantities of monomers such as vinyl ester-based monomer. Any oneof batch saponification, continuous saponification on a belt andtower-type continuous saponification may be used for such asaponification method in accordance with an intended saponificationdegree and the like. Preferably, tower-type saponification under a fixedpressure is used for the reason that the amount of alkali catalystduring saponification is reduced and a saponification reaction easilyproceeds with high efficiency.

Pressure during saponification is selected from the range of 0.1 to 0.8MPa although it depends on an intended ethylene content. Asaponification temperature is 80° to 150° C., and preferably 100° to130° C. Saponification time is selected from the range of 0.5 to 3hours.

Thus, an alcohol solution of EVOH resin is obtained. Such a solution maybe as it is. Preferably, water is directly added to the solution or theconcentration of the alcohol solution of the saponified product isadjusted as appropriate after the addition of water, so that a solutionfor the production of strands is produced as an alcohol/water solution.Thereafter, the solution is extruded and precipitated in the form ofstrands into the coagulating bath of water, a water/alcohol (mixed)solution or the like.

The precipitated strands are then cut into pellets. The pellets arerinsed with water and dried, so that the pellets of EVOH resin areproduced.

Known drying methods may be employed as the aforementioned method ofdrying the EVOH resin pellets. Specific examples of the drying methodinclude a ventilation drying method and a fluidized drying method. Also,different drying methods may be employed for multi-stage drying. Inparticular, a drying method in which the fluidized drying method is usedin the first stage and the ventilation drying method is used in thesecond stage is preferred because it provides good color tones of thepellets and molded parts produced using the pellets. A dryingtemperature is not particularly limited, but a temperature on the orderof 60° to 150° C. is generally employed as the drying temperature. Thetemperature may be increased as the drying process proceeds. Also,circulating an inert gas such as nitrogen gas during the drying processis preferred because it provides good color tones of the molded parts.

By supplying and circulating an inert gas, e.g. nitrogen gas (N₂ gas),as needed to and in a drying container, the amount of volatile matter ofthe EVOH resin pellets obtained in the pelletizing step is reduced toless than 0.3 part by weight per 100 parts by weight of EVOH resincomposition at an end product level. The volatile matter is obtained bycalculating a change in weight after the drying of the pellets at 150°C. for 5 hours (including alcohol).

The absolute specific gravity of the aforementioned EVOH resin pelletsis generally 1.0 to 1.4. The bulk specific gravity of the aforementionedEVOH resin pellets is generally 0.5 to 0.9.

As mentioned earlier, after being subjected to hot air drying which isthe final stage of the aforementioned manufacturing steps, the EVOHresin pellets subjected to the aforementioned pellet drying step arecharged into the pellet transport container (a closed tank of a trailerfor granules, a bulk vehicle and the like) including the aforementionedpressurizing means while remaining at a high temperature (approximately60° to 150° C.), and transported, with the openings of the tank sealed,for the purpose of avoiding the moisture absorption of the pelletsduring the transport and storage of the pellets.

In the method of transporting the EVOH resin pellets according to thepresent preferred embodiment, there also arises a conventionalphenomenon such that a negative pressure is developed in the large-sizedpellet transport container as mentioned above as the temperature of thepellets and the increased temperature of the air in the containerdecrease during the transport of the pellets after the hot pellets(approximately 60° to 150° C.) are directly charged into the containerto fill the container and the container is closed as it is. However, themethod of transporting the pellets according to the present preferredembodiment includes the “pressurizing means” which supplies the dry gas(nitrogen gas) to the aforementioned pellet transport container asmentioned above to always maintain the internal pressure of the pellettransport container at a pressure of more than 1 atm and not more than100 atm (101.3 to 10,130 kPa). This prevents outside air containing muchmoisture from entering the container to maintain the aforementioned EVOHresin pellets in a dry low-humidity state obtained in the early stage ofthe charging. This configuration also improves the transport efficiencyof the pellets while maintaining the quality of the EVOH resin pellets.

Further, the transported EVOH resin pellets do not have a poorappearance resulting from the foaming of moisture and the like during asubsequent molding process of films and the like, so that the yield ofthe processed products is improved. This improves the quality of theEVOH resin as the end product and the molded parts produced using theEVOH resin, and reduces the total costs of the molded parts producedusing the EVOH resin pellets in combination with the improvement in theaforementioned pellet transport efficiency (reduction in raw materialcosts).

In the aforementioned preferred embodiment, the trailer having the tankfor powder and granular materials, the bulk loading vehicle, the tanktruck and the like are illustrated as examples of the closed typelarge-sized tank (pellet transport container) for transporting the EVOHresin pellets. However, other forms including a container form mountableon trains, ships, aircraft and the like and not limited to theaforementioned form may be used for the hermetic container (sealedcontainer) used for the mass transport.

The method of transporting the pellets to the pellet transport containermay include the transport using a conveyor and the like in addition tothe aforementioned air transport. Further, the temperature of thepellets encased into the pellet transport container is generallyapproximately 60° to 150° C. (pellet temperature), preferablyapproximately 70° to 140° C., and more preferably approximately 80° to130° C. The encasing of the pellets at too high of a pellet temperatureinto the container tends to cause a high negative pressure to bedeveloped after the temperature in the container is decreased to roomtemperature.

It is desirable that the time required for the transport of the EVOHresin pellets is held down generally to 1 to 7 days, and preferably to 1to 3 days, although it depends on the distance between plants and thetransport means.

Examples

Next, an example of the present invention will be described in furtherdetail. The present invention is not limited to the example to bedescribed below unless they exceed the subject matter of the presentinvention.

In the example, the term “part(s)” means “part(s) by weight.”

Production of EVOH Resin Pellets

A water/methanol (mixed at water/methanol=40/60 by weight) mixedsolution (60° C., an EVOH concentration of 45 wt %) of an EVOH (anethylene content of 34 mol %, a saponification degree of 99.5 mol %, anda MFR of 20 g/10 min (210° C., a load of 2,160 g)) was extruded in theform of strands into a water bath maintained at 5° C. so as to becoagulated. Thereafter, the strands were cut with a cutter (pelletizer)to provide EVOH in the form of porous pellets (a diameter of 4 mm and alength of 4 mm).

Next, the obtained EVOH in the form of porous pellets was rinsed withwater. Thereafter, the EVOH in the form of porous pellets was chargedinto a water solution containing 0.3 wt % of boric acid and 0.1 wt % ofsodium acetate, and agitated at 35° C. for approximately 4 hours.Further, the EVOH in the form of porous pellets was dried at 75° C. for3 hours in a batchwise tower-type fluidized-bed dryer, and thereafterdried at 125° C. for 18 hours in a batchwise airflow tray dryer. Thisprovided EVOH resin pellets containing 0.03 part of boric acid in boronequivalent and 120 ppm of sodium acetate in sodium equivalent.

The moisture percentage (percentage of moisture content) of the EVOHresin pellets obtained immediately after the drying was 0.09 wt %. TheEVOH resin pellets which remained at a high temperature (120° C.) afterthe aforementioned drying process were immediately charged into a pellettransport container (a closed tank of a trailer for granules) includinga pressurizing means for the purpose of avoiding the moisture absorptionof the pellets during the transport and storage of the pellets.

Transport of EVOH Resin Pellets

Immediately after the aforementioned drying process, 21,000-kg EVOHresin pellets (at a temperature of 120° C.) were charged into the tankof a trailer (with a volume of 46 m³, a material of stainless steel, apellet insertion port of ¾ inch in size, a pellet take-out port of ¾inch in size, and closing mechanisms for the pellet insertion port andthe pellet take-out port being block valves) including the pressurizingmeans having a nitrogen cylinder by using an air transport apparatusutilizing wind power. The pellet filling percentage in the tank of thetrailer in this example was approximately 50%.

After the openings of the tank of the trailer were closed, theaforementioned pressurizing means was put into operation to supplynitrogen gas until a predetermined pressure was reached. With the stateof the predetermined pressure maintained, the trailer transported thepellets. During the transport, the cylinder is periodically replacedwith another so that the supply of the nitrogen gas from thepressurizing means is prevented from being interrupted or stopped.

Changes in “pressure in the tank” during the actual transport of thepellets and transitions of sampled “moisture percentage (percentage ofmoisture content) of pellets” are shown in Table 1 below.

TABLE 1 Transport Time After After After Early After 8 16 24 32 StageHours Hours Hours Hours Pressure in 1.68 1.61 1.54 1.48 1.37 Tank (atm)Percentage 0.09 0.09 0.09 0.09 0.09 of Moisture Content of Pellets (wt%)

Table 1 shows that the interior of the pellet transport container(closed tank of the trailer for granules) is always maintained in astate of higher pressure than the ambient atmosphere during thetransport by the operation of the pressurizing means. This shows thatthe EVOH resin pellets in the transport container do not absorbmoisture, so that the percentage of moisture content in the early stage(during the tank charging) is held. Thus, the method of transporting theEVOH resin pellets in this example is capable of transporting thepellets in large quantities at one time while maintaining the quality ofthe EVOH resin pellets as obtained immediately after the productionthereof.

Although specific forms in the present invention have been described inthe aforementioned example, the aforementioned example should beconsidered as merely illustrative and not restrictive. It iscontemplated that various modifications evident to those skilled in theart could be made without departing from the scope of the presentinvention.

The method of transporting EVOH resin pellets is capable of transportingthe pellets in a dry state in large quantities at one time whilepreventing the pellets being transported from absorbing moisture.Therefore, the transport method improves the transport efficiency of thepellets while maintaining the quality of the pellets.

1. A method of transporting saponified ethylene-vinyl ester-basedcopolymer pellets comprising: maintaining an interior of a hermeticcontainer in a state of higher pressure than ambient atmosphere during atransport of the saponified ethylene-vinyl ester-based copolymer pelletsencased in the hermetic container.
 2. The method according to claim 1,wherein a dry gas with a moisture percentage of not more than 0.8 wt %is used for applying pressure to the interior of the hermetic container.3. The method according to claim 2, wherein the dry gas is nitrogen gas.4. The method according to any one of claim 1, wherein internal pressureof the hermetic container during the transport is more than 1 atm andnot more than 100 atm.
 5. The method according to claim 1, wherein avolume of the hermetic container is in a range of 30 to 60 m³.
 6. Amethod of transporting saponified ethylene-vinyl ester-based copolymerpellets comprising the steps of: encasing the saponified ethylene-vinylester-based copolymer pellets in a hermetic container to close thehermetic container, the hermetic container including a pressurizer forapplying pressure to the interior of the container; transporting thehermetic container to a destination; and maintaining the interior of thehermetic container in a state of higher pressure than ambient atmosphereby using the pressurizer for applying pressure to the interior of thehermetic container during the transporting step.
 7. The method accordingto claim 6, wherein a dry gas with a moisture percentage of not morethan 0.8 wt % is used for applying pressure to the interior of thehermetic container.
 8. The method according to claim 7, wherein the drygas is nitrogen gas.
 9. The method according to claim 6, whereininternal pressure of the hermetic container during the transport is morethan 1 atm and not more than 100 atm.
 10. The method according to claim6, wherein a volume of the hermetic container is in a range of 30 to 60m³.